Atmospheric mixing and the CO₂ seasonal cycle

Atmospheric mixing is determined by such factors as advection and diffusion, planetary boundary layer (PBL) depth, and cloud transport‐together they determine an effective ’mixing volume’ to which CO 2 is then added or removed. In this study a mathematical model is developed to quantify the key factors determining the local ’mixing volume’ and hence the seasonal cycle of atmospheric CO 2 . It was found that the seasonal variation in horizontal advection is more important than the seasonal variation in PBL depth in determining the local mean and seasonal variation in atmospheric CO 2 and that cloud transport plays a minor role.